Dielectric ceramic composition, ceramic capacitor using the composition and method of producing thereof

ABSTRACT

The present invention provides a dielectric ceramic composition, a capacitor using the composition and the producing method, of having a lower dielectric loss and a stable characteristics in high frequency bandwidth, and enabling to use a base metal or a carbon-based material as an electrode material by allowing sintering at a low temperature, thereby resulting in lower cost.  
     The dielectric ceramic composition according to present invention, is characterized in comprising a main component of formula Sr x Ca 1-x (Zr y Ti 1-y )O 3  (where 0.7≦x≦1; 0.9≦y≦1) to which MnO 2  of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi 2 O 3 , PbO and Sb 2 O 3  and a glass component of 0.5-10 wt % are added based on the weight of the main component.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a dielectric ceramic composition, more particular to a dielectric ceramic composition, a ceramic capacitor using the composition and the producing method, thereof having a lower dielectric loss and stable characteristics in high frequency region, and enabling to use a base metal or a carbon-based material as an electrode material by allowing sintering at a low temperature, and thereby reducing the production cost.

[0002] Conventionally, a dielectric property of a ceramic provides a ceramic capacitor having larger capacitance and being more miniature in size. The ceramic capacitor may be made of a material selected from TiO₂ having a rutile structure, BaTiO₃, MgTiO₃, CaTiO₃ and SrTiO₃, having a perovskite structure and the mixture thereof.

[0003] This ceramic capacitor may be classified into a platelike type and a laminate type. The platelike type capacitor is produced by forming said material powder into some shaped body, such as pellet (disc), rod (cylinder) or chip (angular), under pressure, sintering the shaped body at 1200° C.-1400° C. to a sintered body, and forming electrode at each surface of the sintered body.

[0004] Also, the laminated type ceramic capacitor is produced by mixing said material powder with organic binder and organic solvent to prepare a slurry, forming green sheets from the slurry through a doctor bladding, printing the pattern of electrode comprising of a noble metal, such as Pt and Pd, on each of the green sheets, subsequently laminating said green sheets in the thickness direction under pressure to form a laminate, and sintering the laminate at 1200° C.-1400° C.

[0005] As described above, however, in the conventional ceramic capacitor, the sintering process must be performed at a high temperature ranging 1200° C.-1400° C., to obtain the sintered body exhibiting a good electric characteristics and having a high density.

[0006] For the laminated ceramic capacitor, particularly, in the case of using a base metal as an electrode material, there has been a problem to oxidize the base metal during the sintering process, which occurs a high resistance layer formation between the ceramic layers. To avoid the problem, the noble metal material, being stable at high temperature, must be employed as an electrode material, thereby resulting in high cost.

[0007] On application of a device for high frequency bandwidth, such as microwave, it is preferred to have a low dielectric loss. And such device is required to have a good electric characteristics such as a quality value (Q), temperature property (this term means temperature changing ratio of the capacity), and a high reliability. However, no current dielectric material meets all the conditions.

[0008] Accordingly, there has been a need in the art to provide a dielectric ceramic composition, ceramic capacitor using the composition and the producing method to solve the problem as described above.

SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a dielectric ceramic composition and a producing method of the dielectric ceramic composition of having a lower dielectric loss and a stable characteristics in high frequency bandwidth, and enabling to use a base metal, such as Cu and W, or a carbon-based material as an electrode material by allowing sintering at a low temperature, thereby reducing the production cost.

[0010] To achieve the above object, the present invention provides the dielectric ceramic composition comprising a main component of formula Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1) to which MnO₂ of 0.05-20 wt %, at least one of 0.001-5wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass component of 0.5-10 wt % are added based on the weight of the main component.

[0011] It is another object of the present invention to provide a ceramic capacitor using the composition and a method of manufacturing the ceramic capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention and wherein:

[0013]FIG. 1 illustrates cross-sectional structural views of a platelike ceramic capacitor in accordance with example 1.

[0014]FIG. 2 illustrates cross-sectional structural views of a laminated ceramic capacitor in accordance with example 2.

DETAILED DESCRIPTION OF THE INVENTION

[0015] According to the present invention, the dielectric ceramic composition is characterized in comprising a main component of formula Sr_(x)Ca_(1-x)(Zr_(y)T_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1), to which MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃, and a glass component of 0.5-10 wt % are added based on the weight of the main component.

[0016] In the preferred embodiment, the dielectric ceramic composition is produced by adding MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass component 0.5-10 wt % based on the weight of the component to a main component of formula Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1). The resulting composition can exhibit a high dielectric constant, a good temperature property and a high quality value (Q). As a result, the dielectric ceramic composition is suitable for using at high frequency bandwidth.

[0017] The mole fraction of Sr is preferably 0.7 (70 mol %) or more, when the composition containing Sr of less than 0.7 is fired at 925° C.-1080° C. The sintering property of the resultant is deteriorated.

[0018] The mole fraction of Ti is preferably 0.1 (10 mol %) or less. When the mole fraction of Ti is more than 0.1, the temperature property as well as the quality factor (Q) are deteriorated.

[0019] MnO₂ is added to the main component as a sintering aid agent for enabling to sinter at a low temperature. The amount of the agent is preferably 0.05-20 wt %. When the amount of MnO₂ is less than 0.05 wt %, it does little function as an additive, resulting in a lower density of the sintered body. When the amount of MnO₂ is more than 20 wt %, the quality value is deteriorated.

[0020] A metal oxide having a low melting point is added to the main component for improving the temperature property. The metal may be at least one selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃. The additive amount is preferably 0.001-5 wt %. When the additive is less than 0.001 wt %, the temperature property cannot be improved. When the additive is more than 5 wt %, the quality value is deteriorated.

[0021] The glass component is added thereto as a sintering aid agent for enabling to sinter at a low temperature. The additive amount is preferably 0.5-10 wt %. When the glass component is less than 0.5 wt %, the temperature property cannot be improved. When the glass component is more than 10 wt %, the quality value is deteriorated.

[0022] The glass component employed in the present invention preferably has a good wettability to the main component Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1) and is softened and/or melted at 925-1080° C. Specifically, such glass component may be ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.

[0023] In second embodiment of the present invention, SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt % based on the weight of the main component are further added to the dielectric ceramic composition to provide another dielectric ceramic composition.

[0024] SiO₂ is used as an additive for improving the temperature property. The amount of SiO₂ is preferably about 0.01-3 wt %. When the amount of SiO₂ is less than 0.01 wt %, the temperature property cannot be improved. When the amount of SiO₂ is more than 3 wt %, the quality value is deteriorated.

[0025] Al₂O₃ is used as an additive for improving the quality value. The amount of Al₂O₃ is preferably about 0.01-5 wt %. When the amount of Al₂O₃ is less than 0.01 wt %, the quality value cannot be improved. When the amount of Al₂O₃ is more than 5 wt %, the temperature property is deteriorated.

[0026] In the third embodiment of the present invention, a rare earth oxide of 0.001-2 wt % is further added to the dielectric ceramic composition to provide another dielectric ceramic composition based on the weight of the main component.

[0027] The rare earth oxide is used as an additive for improving the temperature property. Preferably, the amount of the rare earth oxide is about 0.001-2 wt %. When the amount of the rare earth oxide is less than 0.001 wt %, the temperature property cannot be improved. When the amount of the rare earth oxide is more than 2 wt %, the quality value is deteriorated.

[0028] The rare earth oxide employed in the present invention has preferably a good wettability to the main composition Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1) and has a grain boundary layer, which is used to improve the sintering property. Specifically, such rare earth oxide may include at least one selected from the group consisting of La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃ and Yb₂O₃.

[0029] Also, the present invention provides a ceramic capacitor with the opposed surfaces comprising one of the dielectric ceramic compositions as described above, each of which an electrode is formed on.

[0030] Further, the present invention provides a ceramic capacitor made by laminating alternatively electrodes and sheets comprising one of the dielectric ceramic compositions as describe above. And the electrodes are characterized in being made of base metal or carbon-based material.

[0031] The ceramic capacitor according to the present invention can exhibits a lower dielectric loss and stable characteristics even at high frequency bandwidth, by using one of the dielectric ceramic compositions as describe above.

[0032] Moreover, it is advantageous that the dielectric ceramic composition can be sintered at a low temperature of 925-1080° C., and an inexpensive metal, such as a base metal and a carbon-based material, can be employed as the electrode, thereby resulting the production cost.

[0033] The base metal having a good conductibility and a high reliability is preferably employed as the electrode, which may be at least one selected from the group consisting of Cu, Ni, W and Mo, and the carbon-based material employed as the electrode may be carbon (amorphous), graphite or the mixture.

[0034] In present invention, a ceramic capacitor fabricating method comprises the steps of forming powder comprising a main component of formula Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1), to which MnO₂ of 0.05-20 wt %, at least one of 0.001-5wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃, and a glass component of 0.5-10 wt % are added based on the weight of the main component, into a bulk or a sheet; and sintering the bulk or a sheet at about 925-1080° C.

[0035] According to the method, a sintering aid agent of MnO₂ and glass component can improve a wettability of a grain boundary layer to bind powder particles and reduce the void fraction during the sintering process even at low temperature of about 925-1080° C. Thus, the sintered body having a high strength and high density can be obtained at the low temperature.

[0036] In another embodiment of the present method, the method may comprise the additional step of providing an electrode on a main surface of the sheet; laminating the sheet in the thickness direction under pressure to form a laminate; and sintering the laminate at about 925-1080° C.

[0037] According to this method, a base metal, such as Cu and Ni, or a carbon-based material, such as amorphous carbon and graphite, is used as an internal electrode, which is less expensive than noble metal, such as Pt and Pd, resulting in the lower cost without deteriorating the characteristics.

[0038] Referring to Figs, the embodiments of the present invention will now be described by examples.

EXAMPLE 1

[0039] Referring to FIG. 1, cross-sectional structural view of a platelike ceramic capacitor in accordance with a first example is shown in FIG. 1. The capacitor comprises a bulk shape dielectric body 1, terminal electrodes 2 formed on the opposed surfaces of the dielectric body 1, lead lines 3 connecting to the terminal electrode, and an epoxy resin 4 encapsulating the dielectric body 1 and the terminal electrode 2.

[0040] The dielectric body 1 is made of a dielectric ceramic composition comprising a main component of formula Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1), to which MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass frit (glass component) of 0.5-10 wt % are added based on the weight of the main component.

[0041] The dielectric body 1 may include one of to the dielectric ceramic composition further containing SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt %, the dielectric ceramic composition further containing a rare earth oxide of 0.001-2 wt %, and the dielectric ceramic composition further containing SiO₂ of 0.01-3 wt %, Al₂O₃ of 0.01-5 wt % and rare earth oxide of 0.001-2 wt %.

[0042] The terminal electrode 2 comprises a conductive material having a high reliability, such as Ag and Ag alloy. Preferably, Ag alloy may include 90 Ag-10 Pd.

[0043] The material of the terminal electrode 2 may also include at least one selected from the group consisting of Cu, Ni, W and Mo, or carbon, graphite or the mixture.

[0044] This ceramic capacitor exhibits a stable dielectric constant (ε), quality factor (Q) and temperature property (Tc) even in high frequency bandwidth.

[0045] The method of manufacturing this capacitor will now be described.

[0046] Each of Powdered SCZT, MnO₂, at least one selected from the group of consisting Bi₂O₃, PbO and Sb₂O₃, glass frit, SiO₂, Al₂O₃ and rare earth oxide were weighed as the predetermined amount to prepare various compositions as shown in Tables 1 and 2. TABLE 1 Main component Sintering (mole fraction) Additive A Additive B tempera- Specimen Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (wt %) (wt %) ture Number Sr Ca Zr Ti MnO₂ Al₂O₃ SiO₂ Glass frit Bi₂O₃ CeO₂ (° C.) 1 1 0 1 0 0 0 0 0 0 0 1050 2 1 0 1 0 0.3 0 0 0.3 1.0 0 1000 3 1 0 1 0 0.3 0 0 3.0 1.0 0 950 4 1 0 1 0 0.3 0 0 11.0 1.0 0 950 5 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 950 6 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 950 7 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 950 8 1 0 0.95 0.05 5.0 0.1 0.05 2.5 6.0 0.01 950 9 1 0 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 950 10 0.99 0.01 1 0 0.3 0 0 0.3 1.0 0 1000 11 0.99 0.01 1 0 0.3 0 0 3.0 1.0 0 950 12 0.99 0.01 0.95 0.05 0.01 0.1 0.05 2.5 0.5 0.01 925 13 0.99 0.01 0.95 0.05 0.3 0.1 0.05 2.5 0.5 0.01 950 14 0.99 0.01 0.95 0.05 5.0 0.1 0.05 2.5 1.0 0.01 950 15 0.98 0.02 0.95 0.05 0.3 0 0 0.3 1.0 0 1000 16 0.98 0.02 0.95 0.05 5.0 0 0 3.0 1.0 0 950 17 0.98 0.02 0.95 0.05 5.0 0 0 10.0 1.0 0 950 18 0.98 0.02 0.95 0.05 5.0 0 0 3.0 5.0 0 950 19 0.98 0.02 0.95 0.05 5.0 0.05 0.05 2.5 0.5 0.01 950 20 0.98 0.02 0.95 0.5 5.0 0.5 0.05 2.5 0.5 0.01 950

[0047] TABLE 2 Main component Sintering (mole fraction) Additive A Additive B tempera- Specimen Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (wt %) (wt %) ture number Sr Ca Zr Ti MnO₂ Al₂O₃ SiO₂ Glass frit Bi₂O₃ CeO₂ (° C.) 21 0.98 0.02 0.95 0.05 5.0 0.5 0.05 2.5 1.0 0.01 900 22 0.98 0.02 0.95 0.05 5.0 0.5 0.05 11.0 1.0 0.01 950 23 0.98 0.02 0.95 0.05 5.0 5.0 0.05 2.5 0.5 0.01 950 24 0.98 0.02 0.95 0.05 5.0 0.1 0.5 2.5 0.5 0.01 950 25 0.98 0.02 0.95 0.05 5.0 0.1 3.0 2.5 0.5 0.01 950 26 0.98 0.02 0.95 0.05 5.0 0.1 0.1 2.5 0.5 0.01 925 27 0.98 0.02 0.95 0.05 0.3 0.1 0.05 2.5 1.0 0.01 950 28 0.98 0.02 0.9 1 5.0 0.1 0.1 11.0 1.0 0.01 925 29 0.98 0.02 0.95 0.05 3.0 0.2 0.3 2.5 0.5 0.001 950 30 0.98 0.02 0.95 0.05 3.0 0.2 0.3 2.5 0.5 2.1 950 31 0.98 0.02 0.95 0.05 3.0 0.2 0.3 2.5 0.5 0.01 1050 32 0.98 0.02 0.85 0.15 3.0 0.2 0.3 2.5 0.5 0.01 950 33 0.95 0.05 0.95 0.05 0.3 0 0 0.3 1.0 0 1000 34 0.95 0.05 0.95 0.05 5.0 0 0 3.0 1.0 0 950 35 0.95 0.05 0.95 0.05 5.0 0 0 10.0 1.0 0 950 36 0.95 0.05 0.95 0.05 5.0 0 0 3.0 5.0 0 950 37 0.95 0.05 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 950 38 0.95 0.05 0.95 0.05 5.0 0.5 0.3 2.5 0.5 0.01 950 39 0.9 0.1 0.95 0.05 5.0 0.1 0.5 2.5 0.5 0.01 950 40 0.9 0.1 0.95 0.05 5.0 0.1 3.0 2.5 0.5 0.01 950 41 0.9 0.1 0.95 0.05 0.3 0.1 0.05 2.5 0.5 0.01 900 42 0.9 0.1 0.9 0.1 5.0 0.1 0.1 2.5 6.0 0.01 925 43 0.8 0.2 0.95 0.05 5.0 0.05 0.05 2.5 0.5 0.01 950 44 0.8 0.2 0.95 0.05 5.0 0.5 0.05 2.5 0.5 0.01 950 45 0.8 0.2 0.95 0.05 5.0 0.5 0.05 2.5 0.5 0.01 900 46 0.8 0.2 0.9 0.1 5.0 0.5 0.3 2.5 0.5 2.1 950 47 0.7 0.3 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 925 48 0.7 0.3 0.95 0.05 5.0 0.1 0.1 2.5 0.5 0.01 925 49 0.7 0.3 0.9 0.1 5.0 0.5 0.1 10.0 0.5 0.01 900 50 0.65 0.35 0.95 0.05 5.0 0.1 0.05 2.5 0.5 0.01 925

[0048] The prepared compositions were wet-milled with water (or organic solvent such as ethanol and acetone) in ball mill for predetermined time, such as 24 hours. The resultant mixture was dehydrated (or removal of the solvent, such as ethanol and acetone) and dried. Specimen comprising different composition from thereof the present invention was prepared as comparison (indicated by  in the Tables 1 and 2).

[0049] Then, the dried mixture was preliminary fired at 550-750° C., for 05-5.0 hours, followed by pulverizing for 1-24 hour with a mortar machine (or automatic pestle) to obtain the fired powder having the desired granularity.

[0050] Subsequently, an appropriate amount of an organic binder was added to the fired powder. The resultant was mixed and granularized uniformly using a mortar machine and a like to obtain granular powder having the desired granularity. Polyvinyl alcohol (PVA) was employed as a organic binder. Other organic binder may include ethylcellulose aqueous solution and acryl resin solution (acryl binder)

[0051] Then, the pellet having a diameter of 20 mm and a thickness of 0.5 mm is formed from the granular powder using a forming machine, followed by firing at 925-1080° C., for 0.5-10 hours under atmosphere, to obtain a disk-shaped dielectric body 1.

[0052] The composition of the present invention was fired at the other temperature to prepare another specimen as comparison (indicated by “” in the Tables 1 and 2).

[0053] Tables 3 and 4 show electric characteristics of each specimen. TABLE 3 Temperature Specimen Dielectric Quality Resistance property(Tc) Number constant (ε) value (Q) (Ω · cm) (ppm/° C.)  1 13 230 1.6 × 10¹¹ 96  2 18 240 1.2 × 10¹² 103  3 23 2300 1.9 × 10¹² 60  4 22 380 1.5 × 10¹² 180  5 28 2680 1.7 × 10¹² 58  6 24 210 1.2 × 10¹¹ 76  7 30 4500 1.9 × 10¹² 40  8 33 180 1.5 × 10¹² 26  9 31 6400 2.1 × 10¹² 35 10 27 310 1.6 × 10¹² 55 11 30 3120 2.3 × 10¹² 42 12 24 310 2.6 × 10¹² 81 13 29 3240 2.1 × 10¹² 37 14 28 2980 1.9 × 10¹² 22 15 26 160 1.5 × 10¹² 26 16 27 1980 1.9 × 10¹² 23 17 21 1600 2.0 × 10¹² 34 18 23 1920 1.1 × 10¹² 29 19 30 5200 1.2 × 10¹² 38 20 31 4800 1.9 × 10¹² 42

[0054] TABLE 4 Temperature Specimen Dielectric Quality Resistance property(Tc) Number constant (ε) value (Q) (Ω · cm) (ppm/° C.) 21 26 315 2.0 × 10¹² 48 22 30 260 1.0 × 10¹¹ 26 23 32 2300 2.3 × 10¹² 60 24 30 6200 2.2 × 10¹² 30 25 29 2100 1.2 × 10¹² 15 26 29 2320 2.0 × 10¹² 26 27 26 1870 1.8 × 10¹² 31 28 28 190 1.6 × 10¹¹ −5 29 31 2600 1.5 × 10¹² 20 30 30 410 1.5 × 10¹¹ 26 31 31 5950 1.9 × 10¹² 20 32 41 360 1.5 × 10¹² −380 33 30 120 1.8 × 10¹² 63 34 31 3680 2.0 × 10¹² 58 35 31 1780 1.8 × 10¹² 47 36 29 1580 1.6 × 10¹² 39 37 29 2400 1.9 × 10¹² 42 38 33 3250 2.0 × 10¹² 26 39 31 2800 1.8 × 10¹² 18 40 30 1960 1.9 × 10¹² 19 41 16 370 1.2 × 10¹¹ 13 42 22 160 1.0 × 10⁹  −9 43 24 1850 1.8 × 10¹² 12 44 26 1260 1.9 × 10¹² 15 45 12 260 1.5 × 10¹¹ 16 46 23 430 1.7 × 10¹² 30 47 23 1150 1.9 × 10¹² −19 48 21 1260 2.0 × 10¹² −26 49 15 170 1.6 × 10¹¹ −95 50 13 120 1.3 × 10¹¹ −120

[0055] Wherein, the dielectric constant (ε) was measured at 25° C. under the condition of frequency of 1 MHz and an input voltage of 1V_(rms). The Q value was measured under the condition of frequency of 1 MHz and an input voltage of 1V_(rms). The temperature property (Tc) was calculated from the following equation

Tc(ppm/° C.)=(C 2−C 1×10 ⁶)/(C 1×(125−25))

[0056] Wherein, the C1 is the capacitance at 125° C. and the C2 is the capacitance at 25° C.

[0057] And the resistance (R(Ω·cm)) was calculated by using the voltage and the current, which were measured on applying a direct voltage of 1000V for 1 minute at 25° C.

[0058] Referring to the result of Tables 3 and 4, the dielectric constant (ε), Q value and temperature property (Tc) were stable even at high frequency in this example, while the characteristics of all the comparisons were deteriorated.

[0059] Further, when the specimen surfaces of these examples were observed through a metallurgical microscope, it will be known that no void was present at grain boundary and a dense sintering body was constructed.

[0060] As described above, according to this example, the dielectric composition exhibiting high dielectric constant, high Q value and good temperature property, can be obtained by adding MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass frit of 0.5-10 wt % to a main component of SCZT based on the weight of the main component and optionally further adding SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt % and rare earth oxide of 0.001-2 wt % thereto. Thus, the dielectric composition is capable of a dielectric capacitor having stable characteristics and improved reliability.

[0061] According to the method of manufacturing the ceramic capacitor, the ceramic capacitor having high density and strength can be provided at the low temperature by forming a bulk or a sheet from powder comprising a main component of SCZT to which MnO₂ of 0.05-20 wt %, at least one 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass component of 0.5-10 wt % are added based on the weight of the component, and which optionally SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt % and rare earth oxide of 0.001-2 wt % are added thereto and firing the sheet or other resultant at 925-1080° C.

EXAMPLE 2

[0062]FIG. 2 illustrates cross-sectional structural view of a laminated ceramic capacitor in accordance with second example. The capacitor comprises a sheet-shaped dielectric layers 11, thin internal electrodes 12 and terminal electrodes 13,14. This laminated ceramic capacitor is comprised of eight dielectric layers 11 and seven thin internal electrodes 12, which are alternatively laminated.

[0063] The dielectric layer 11 is made of sheet-shaped ceramic composition comprising a main component of SCZT to which MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass frit (glass component) of 0.5-10 wt % are added based on the weight of the main component.

[0064] Alternatively, the dielectric layer 11 may include one of the dielectric ceramic composition further containing SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt %, the dielectric ceramic composition further containing rare earth oxide of 0.001-2 wt %, and the dielectric ceramic composition further containing SiO₂ of 0.01-3 wt %, Al₂O₃ of 0.01-5 wt % and rare earth oxide of 0.001-2 wt % is added.

[0065] The internal electrode 12 and the terminal electrodes 13,14 include a conductive material having high reliability, for example, Cu, Ni, W and Mo, or carbon, graphite or the mixture.

[0066] This laminated ceramic capacitor exhibits a stable dielectric constant (ε), quality factor (Q) and temperature property (Tc) even in RF region.

[0067] The method of manufacturing this laminated ceramic capacitor will be described now.

[0068] Each of powdered SCZT, MnO₂, at least one selected from the group of consisting Bi₂O₃, PbO and Sb₂O₃, glass frit, SiO₂, Al₂O₃ and rare earth oxide were weighed as the predetermined amount. Each composition was wet-milled with water (or organic solvent such as ethanol and acetone) in ball mill for predetermined time, such as 24 hours. The resultant mixture was dehydrated (or removal of the solvent, such as ethanol and acetone) and dried.

[0069] Then, an appropriate amount of an organic binder was added to the dried powder. Subsequently, the resultant powder was mixed using a mortar machine, a mixing mill and a like to obtain a slurry having desired viscosity. Polyvinyl alcohol (PVA) was employed as the organic binder. Other organic binder may be employed, such as ethylcellulose aqueous solution and acryl resin solution (acryl binder).

[0070] Then, the slurry was deaired and formed into sheets through doctor blading to obtaining a ceramic green sheet. A conductive paste was printed as desired pattern on the green sheet. Thereby the internal electrode layer was formed on the green sheet. The conductive paste may include alloy containing at least one selected from a group consisting of Cu, Ni, W and Mo, or carbon, graphite or the mixture.

[0071] Particularly, the conductive paste employed in present invention may be a carbon paste made from a mixture powder of a carbon powder and a graphite powder, W paste and Mo paste, as well as a Cu paste, which is obtained by adding organic binder, dispersing agent, organic solvent and, if necessary, reducing agent, to Cu powder and then mixing thereof.

[0072] Then, the green sheets were laminated in the thickness direction under pressure to form a laminate, followed by firing at 925-1080° C., under inert gas atmosphere, such as N₂ gas, or N₂—H₂ reductive atmosphere. Each terminal electrode was then formed on the opposed surfaces of the laminate.

[0073] Thus, the laminated ceramic capacitor can be produced through the step of laminating alternatively the dielectric layer 11 and the internal electrode 12.

[0074] As described above, for the laminated ceramic capacitor according to this example, it can exhibit high dielectric constant, high Q value and good temperature property, since it is comprised of the composition obtained by adding MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass frit of 0.5-10 wt % to a main component of SCZT based on the weight of the component and optionally further adding SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt % and a rare earth oxide of 0.001-2 wt % thereto. Thus, the laminated ceramic capacitor is capable of exhibiting stable characteristics and improved reliability in high frequency.

[0075] According to the method of manufacturing the laminated ceramic capacitor, the laminated ceramic capacitor having high density and strength can be produced by forming the internal electrode on green sheet comprising a main component of SCZT to which MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass component of 0.5-10 wt % are added based on the weight of the component, and which optionally SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt % and a rare earth oxide of 0.001-2 wt % are added thereto, laminating the green sheet in the thickness direction to form a laminate, firing the laminate at 925-1080° C. under inert gas atmosphere or N₂—H₂ reductive atmosphere. Thus, an inexpensive base metal and carbon-based material can be used as an electrode material, in lie of a noble metal, such as Pt or Pd, since the laminated ceramic capacitor is produced by the process of firing at relatively low temperature. Therefore, the manufacturing method according to the present invention can realize the lower cost without deteriorating the characteristics.

[0076] As described above, according to the dielectric ceramic composition of the present invention, the dielectric composition is produced by adding MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass frit of 0.5-10 wt %, to a main component of SCZT based on the weight of the component and optionally further adding SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt % and a rare earth oxide of 0.001-2 wt % thereto. Thus, the dielectric composition can exhibit high dielectric constant, high Q value and good temperature property, resulting in the stable characteristics and improved reliability at high frequency region, such as microwave.

[0077] For a ceramic capacitor, according to the present invention, the capacitor can exhibit a low dielectric loss even at high frequency bandwidth, since it is made of the dielectric ceramic composition. Therefore, the present capacitor is suitable for RF device. The present capacitor can also realize the lower cost without deteriorating the characteristics, since an inexpensive base metal or carbon-based material can be used as an electrode material due to the low sintering temperature of 925-1080° C.

[0078] While the invention has been described in its preferred embodiments, this should not be construed as limitation on the scope of the present invention and can be modified and changed to other various embodiments. Accordingly, the scope of the present invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents. In second example, eight dielectric layers and seven internal electrodes are laminated to form a laminate, but the number of the dielectric or internal electrode may be changed to be suitable for the desired capacitor and characteristics. 

What is claimed is:
 1. A dielectric ceramic composition comprising a main component of formula Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1), MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃, and a glass component of 0.5-10 wt %, based on the weight of the main component.
 2. The dielectric ceramic composition according to claim 1 , further comprising SiO₂ of 0.01-3 wt % and Al₂O₃ of 0.01-5 wt %.
 3. The dielectric ceramic composition according to claim 1 , further comprising a rare earth oxide of 0.001-2 wt %.
 4. The dielectric ceramic composition according to claim 2 , further comprising a rare earth oxide of 0.001-2 wt %.
 5. The dielectric ceramic composition according to claim 1 , wherein the glass component is ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.
 6. The dielectric ceramic composition according to claim 2 , wherein the glass component is ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.
 7. The dielectric ceramic composition according to claim 3 , wherein the glass component is ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.
 8. The dielectric ceramic composition according to claim 4 , wherein the glass component is ZnO—SiO₂ based glass or Li₂O—Al₂O₃—SiO₂ based glass.
 9. The dielectric ceramic composition according to claim 3 , wherein the rare earth oxide is at least one selected from the group consisting of La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, and Yb₂O₃.
 10. The dielectric ceramic composition according to claim 4 , wherein the rare earth oxide is at least one selected from the group consisting of La₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, and Yb₂O₃.
 11. A ceramic capacitor comprising: a ceramic body of the dielectric ceramic composition according to claim 1 ; and electrodes formed respectively on opposed surfaces of the ceramic body.
 12. The ceramic capacitor according to claim 11 , wherein said electrode is base metal or carbon-based material.
 13. A ceramic capacitor comprising: a ceramic body of the dielectric ceramic composition according to claim 2 ; and electrodes formed respectively on opposed surfaces of the ceramic body.
 14. A ceramic capacitor comprising: a ceramic body of the dielectric ceramic composition according to claim 3 ; and electrodes formed respectively on opposed surfaces of the ceramic body.
 15. A ceramic capacitor comprising: a ceramic body of the dielectric ceramic composition according to claim 4 ; and electrodes formed respectively on opposed surfaces of the ceramic body.
 16. A ceramic capacitor comprising: a ceramic body of the dielectric ceramic composition according to claim 5 ; and electrodes formed respectively on opposed surfaces of the ceramic body.
 17. A ceramic capacitor comprising: a plurality of sheets of dielectric ceramic composition according to claim 1 ; and a plurality of electrodes on each of sheets, wherein the sheets and the electrodes are alternatively laminated.
 18. The ceramic capacitor according to claim 17 , wherein said electrode is base metal or carbon-based material.
 19. A method of producing a dielectric ceramic composition, comprising the steps of: forming a bulk or a sheet with powder including a main component of formula Sr_(x)Ca_(1-x)(Zr_(y)Ti_(1-y))O₃ (where 0.7≦x≦1; 0.9≦y≦1), to which MnO₂ of 0.05-20 wt %, at least one of 0.001-5 wt % selected from the group consisting of Bi₂O₃, PbO and Sb₂O₃ and a glass component 0.5-10 wt % are added based on the weight of the main component; and firing the bulk or the sheet at 925-1080° C.
 20. The method according to claim 10 , further comprising: providing an electrode on a main surface of the sheet; laminating the sheet in the thickness direction under pressure to form a laminate; and firing the laminate at 925-1080° C. 